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Ben Brown, Alan Johnston; Interactions between dynamic facial features. Journal of Vision 2015;15(12):146. doi: 10.1167/15.12.146.
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© ARVO (1962-2015); The Authors (2016-present)
Dynamic facial expressions entail coordinated movement of multiple facial features. Cook et al. found illusory slowing of eye blinks in the presence of mouth movement, arguing against independent processing in favour of global encoding of dynamic facial features (Cook, Aichelburg & Johnston, Psychological Science, in press). The present work extends the search for feature motion interactions from perception to performance. Principal Component Analysis occlusion studies highlight the importance of the eyebrow and mouth regions for determining global configuration. We asked whether the detection threshold for misaligned eyebrow movement might change in the presence of mouth movement. In a 2AFC design participants viewed two animated facial avatars, displayed for 3 seconds, either side of fixation, whose eyebrows oscillated sinusoidally at 1.5Hz. The standard’s eyebrows moved in phase, while the comparison’s were offset by between 1 – 30 degrees of phase angle (increments of around 5 degrees; standard/comparison position switching randomly). Participants judged which face’s eyebrows were misaligned. The 75% point on the fitted psychometric function was taken as the dynamic misalignment discrimination threshold. In separate blocks both mouths were either closed or oscillating at 1.5Hz, and faces were upright or inverted. The inversion manipulation allowed us to differentiate between face-specific and lower-level mechanisms. Thresholds for 4 out of 5 participants increased in the presence of mouth movement by around 3.5 degrees of phase. Mouth movement therefore interferes with eyebrow movement discrimination, despite the spatial separation. The threshold shift either disappeared or reversed for inverted faces (mean shift around -0.9 degrees of phase). Face-specific processes can therefore be implicated in causing the interference as opposed to distraction, crowding or other low-level interactions. It would appear that the grouping of mouth movement with eyebrow movement disrupts the capacity of participants to discriminate eyebrow motion patterns.
Meeting abstract presented at VSS 2015
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